254 THE AMERICAN MONTHLY [November, 



two slips together, and it leaves a ledge for the preparation to rest on. 

 Specimens, therefore, if mounted on glass covers seven-eighths of an 

 inch square, drop into the frame or carrier, and can be turned and ex- 

 amined from each side. 



Such are a few of those preliminary details which are necessary for 

 elementary work. After having examined simple objects requirmg no 

 special preparation, one may pass on to those needing more complex 

 treatment. 



{To be coitiiniied.~\ 



Protective Inocul.atioiis. 



By B. M. BOLTON, M. D., 



BKOOKLlfN, N. Y. 



[From Brooklyn Medical Journal, June-September, 1890.] 



Pasteur was the first to make extensive experiments with a view to 

 obtaining vaccines for protective inoculations for various infectious 

 diseases. He was led to these experiments by Jenner's discovery of 

 vaccination for small-pox, but it is evident that Pasteur's inoculations 

 differ from vaccination for small-pox, for Pasteur uses cultures of the 

 micro-organism, causing the very disease for which he inoculates. In 

 vaccination for small-pox, as is well known, the infectious material of 

 a disease similar to, but not identical with, small-pox is used. Pas- 

 teur's inoculations are, therefore, rather to be compared to the inocu- 

 lations formerly in use where small-pox virus was used to inoculate 

 with. The object Pasteur seeks to obtain is to so modify the infectious 

 material that it will produce only a inild form of the disease in ques- 

 tion. This problem is very difficult of solution, and the most serious 

 obstacle is the variable susceptibility, not only of difl'erent races of ani- 

 mals, but also of the different individuals of the same species ; infec- 

 tious material which causes a mild attack of the disease in one animal 

 sometimes — exceptionally, it is true — causing death in another animal 

 of the same species. Although this difficulty has not yet been over- 

 come the possibility of attenuating infectious material, so that it will 

 produce only a mild form of disease, is well established. As yet these 

 inoculations are of more interest from a scientific than from a practi- 

 cal point of view, at least in human medicine, and the practical utility 

 of protective inoculations in animals is still an open question. 



Pasteur found that the artificial attenuation of pathogenic micro- 

 organisms can be effected in two ways. In the first place by the use 

 of some agent injurious to the bacteria, such as heat, chemical agents, 

 etc. ; these cause, according to Fliigge, a degeneration of the organ- 

 isms, and the virulence returns in a longer or shorter time when the 

 organisms are again placed under favorable conditions. In the second 

 place attenuation may be effected by cultivating the organisms for some 

 length of time under unusual conditions — for example, in the bodies of 

 animals not susceptible to natural infection ; the attenuation obtained in 

 this way seems to be much more durable than that obtained by the first 

 method and not so likely to be lost by cultivating the attenuated cult- 

 ures under normal conditions. Besides the methods of inoculation 

 with attenuated cultures, it has been attempted to render animals im- 

 mune by inoculation of the products of the growth of bacteria, /. <?., 

 the so-called ptomaines. 



