3,000 diameters, in the lower part less. The bacillus rods them. selves vary from to robo of an inch in diameter.*

The vibrio resembles the bacillus, but is flexible, often curved, like the letter S. Vibriones are the thread-like forms; they move by a vibrating motion, hence the name. Any one familiar with microscopical examination of urine has often seen different species of them.

The spirillum is explained by its name, the spiral form. The spores closely resemble the comma used in punctuation. A species is associated with relapsing fever.

DESCRIPTION OF THE PLATE.

The plate, in a general way, illustrates the life history of all microbes. The two principal methods of multiplication are shown by the development of spores and transverse fission. Figs. 1 to 3 show the spores of Bacillus anthracis, Fig. 2 binary fission, and Fig. 3 the zooglea form. The development of the spore into a complete rod or bacillus is shown in Fig. 4, the resulting bacillus in the next figure, which shows the commencement of transverse fission complete in Fig. 6, which has lengthened into a filament at Fig. 8. At the next figure (nine) the protoplasm of the interior has commenced to contract, and the lines of fission where the filament is to break up into rods are shown. The contraction of the protoplasm into spores is shown in Figs. 9 to 14, and the escape of the spores by the breaking up of the filament into rods, i. e., bacilli, is shown in the next three figures. The second subdivision

is seen in Figs. 10 and 11, and the complete germs in Fig. 14.

In Fig. 22 the modifying effects of cultivation at a fixed temperature are seen in the long filament which results. The sporebearing filaments are often smaller than the others, as seen in Fig. 26, also Figs. 20 and 21. A curious form is seen in Fig. 23, a "double spiral rope work," instead of the usual zooglea mass shown in Fig. 19, formed from the bacilli shown in Figs. 20 and 21. The development of these cultivated spores is shown in Fig. 25.

The rope-work has been compared to a tangled skein of silk. The silken threads, studded with brightly refractive spores, present a beautiful appearance under the microscope.

taken.

Carpenter on the Microscope," 6th edition, from which the plate is

METAMORPHOSIS OF GERMS.

It has been asserted that innocent bacteria may be developed into malignant forms by changing their food-supply, and in other ways. Thus one of the germs found in the mouth may be transformed into the one that kills by producing septicemia, that is, blood poisoning. The bacillus from an infusion of hay may be converted into the one that produces anthrax by feeding it with egg albu mum and the serum of the blood. By varying temperature, supply of oxygen, and by successive cultivations qualities may be changed almost at will. This has been done with a large number of bacteria, a few are alluded to above as illustrations. That malignancy and infectiousness have been placed under control, will be fully shown farther on.

In carefully studying the life-history of the Bacillus anthracis, microscopists have found that the rod, in living tissues, multiplies indefinitely by a process of transverse fission but it is not proved to lengthen out into filaments. If a moderate temperature, however, be kept up for several hours after death, and with other conditions favorable, it may assume the filamentous form. But in a short time, the protoplasm, of which the filament is largely composed, gradually contracts, segregation into globular masses occurs, and thus myriads of spores are formed. These in turn may either germinate and at once grow into rods again, or subdivide into four distinct sporules, which then germinate, and form rods, similar to the original type, thus completing a vegetative cycle of existence.

But when these bacilli are cultivated under artificial conditions, on the warm stage of the microscope, they have sometimes been observed to become mobile, but after being alternately in motion and at rest for some hours, the rod lengthens out into an exceedingly long filament, which has become much more "attenuate than ever found under natural conditions, as shown in Fig. 22. In this state the protoplasm of the filament undergoes similar changes as before, but undoubtedly with altered properties.

MODE OF ACTION.

The production of disease by bacteria, or their germs, has been explained in several different ways, the following being the principal. First, that the germs are the carriers only of contagion or infec

tion. Second, that the necrobiotic changes they induce in the tis sues produce a chemical virus which causes the disease. Third, that the germs penetrate the tissues directly, enter the blood-vessels and permeate the corpuscles, and thus produce disease. Fourth, that the innocent germs in the body acquire malignancy, consequently increased powers of motion, penetration, and rapidity of growth, thus using the tissues and fluids of the body for their own nourishment. However this may be, it is true that innocent germs use the body as a pasture-ground, hence the probability that disease-germs may do the same. The fact that bacteria can be transferred from animal to animal while their life history is so ob scure, at least that of the greater number, and can be so modified in their characteristics, strengthens the probability still further that these organisms play a causative role in the production of infective disease.

VARIOLOUS INOCULATION.

Early in the sixteenth century, when the ravages of small-pox were rife among the people and had attracted a wide-spread interest, the inoculation of the active virus was resorted to, with a view of diminishing the fatal effects of the malady. This method of producing the disease at will, in a milder form, which experience, gathered from the secrets of the past, had shown was equally effi cacious as a protective measure, became a common practice in Persia, Hindostan, and other oriental nations, and received the endorsement of the most enlightened physicians of the age:

Variolous inoculation was introduced into England in 1722, by Mrs. Mary Wortley Montague, wife of the Embassador to Turkey, who, on her return home, had her daughter inoculated, according to the almost universal custom which they had observed in the East, of having the children submitted to this operation every autumn, and where their son, five years previously, had passed through this induced malady with favorable results. This made a deep impression on the minds of the English people, who were already very solicitous about the matter. Dr. Keith, with much confidence and anxiety, followed the example by the inoculation of his son, and this new practice therefore, under such sanction, soon became popular throughout the British isles.

Caroline, Princess of Wales, one of whose daughters, Princess Anne, had nearly died from small-pox, which very much disfigured

her, became anxious that the rest of her children should be protected by inoculation against such a misfortune. But as she had not acquired sufficient confidence, some further demonstrations became necessary, and George the First offered pardon to six condemned criminals, if they would consent to be inoculated for the good of the public. Five of them were favorably affected, the sixth not at all, and a seventh felon escaped the ordeal of the gallows by allowing a few small-pox scabs to be thrust up her nose as an experiment.

After variolation had been successfully practiced on several children at the parish of St. James, the Princesses Amelia and Caroline submitted to the operation, which resulted in a very satisfactory manner. As the practice, however, became more general, a fatal case now and then occurred, so that at the end of eight years, out of 845 inoculations, 17 had proved fatal. Thus showing that this induced affection, instead of being perfectly harmless, as it was at first supposed, had been attended with two per cent. of mortality, even under the most favorable circumstances. But to make this practice more availing in a sanitary point of view, a small pox hospital was erected in 1746, for the benefit of the poor, who had already contracted the disease, and for the free inoculation of the children, as well as for adults who had hitherto escaped the disease. This charitable movement, however, greatly increased the mortality from small-pox, which for ten years, including four after the opening of the institution, had averaged 72 in every 1,000; increased during the second decade, to 103, and in the next, to 111; from which we are forced to conclude, that the inoculation of the unmodified virus has a tendency to disseminate the germs of this loathsome and contagious malady.

The protective inoculation of small-pox was initiated in this country about the middle of the last century, and for a time was extensively practiced by a privileged class, who, in those days, united the office of priest and physician. During the winter of 1777 and '78, twelve hundred persons were inoculated at Middletown, Conn., and pock-houses were established in many towns in this and other states. But this method of protection, notwithstanding its many advocates on both sides of the Atlantic, was superseded in the progress of comparative pathology, by that very efficient, safe, and much more wholesome practice of Vaccination.