Mat 3, 1907] 



SCIENCE 



699 



forms which leave no doubt that they be- 

 long to a liYing structure. This is espe- 

 cially true of the recognized pathogenic 

 protozoa of man and the higher animals. 

 Hence some zoologists have taken the 

 ground that when a protozoon is encoun- 

 tered under the microscope its character- 

 istic forms can be recognized at a glance. 

 Nevertheless, there has been a constant en- 

 deavor to force the acceptance, as protozoa, 

 of various specific intracellular bodies 

 found in cancer, rabies, the exanthemata, 

 and certain related diseases of lower ani- 

 mals, although the structure of these bodies 

 is not clearly protozoan. The danger of 

 accepting these doubtful bodies as protozoa 

 lies in the fact that not only in these dis- 

 eases, but in others of known bacterial 

 origin (diphtheria, glanders), there are 

 peculiar intracellular degenerative prod- 

 ucts, more or less specific of each disease 

 and organ, all of which closely resemble 

 some forms of protozoa. Hence in the ab- 

 sence of entirely characteristic trophozo- 

 ites, sporocysts, or spores, it is unsafe to 

 regard any of the bodies as protozoa. The 

 morphological study of the cell inclusions 

 in cancer, variola, scarlatina, measles, 

 rabies, clavelle, contagious epithelioma of 

 birds, etc., has not led to a definite result 

 in any of them. 



In the absence of fully characteristic 

 protozoan forms, the circumstantial or col- 

 lateral evidence becomes of decisive impor- 

 tance. This collateral evidence in cancer 

 is practically conclusive against the proto- 

 zoan nature of the disease, and of the vari- 

 ous cancer parasites. In the exanthemata 

 it does not seem favorable to the protozoan 

 nature of the bodies described as parasites, 

 nor to the protozoan theory of the origin 

 of these diseases. In rabies there are some- 

 what more definite indications pointing to 

 the protozoan nature of the disease and of 

 the Negri bodies, but this evidence is still 



inconclusive. The study of diseases of un- 

 known etiology exclusively from the proto- 

 zoon standpoint is to be deprecated. There 

 are some grounds for supposing that the 

 above diseases, except cancer, may be due 

 to invisible but not necessarily sub-micro- 

 scopic organisms or even to peculiar actions 

 of well-known bacteria. The virus in the 

 exanthemata, and probably in rabies, is 

 perhaps connected with the specific cellular 

 products of these diseases, but is itself of a 

 nature not understood, and yet unparal- 

 leled among known protozoa. 



Immunity against Trypanosomes : F. G. 



NOVY. 



It is an established fact that rats which 

 have recovered from an infection with T. 

 Lewisi are immune to subsequent inocula- 

 tion with that species of flagellate. The 

 same holds true for cattle, sheep, goats, etc., 

 that have recovered from the infection 

 caused by the pathogenic trypanosomes, 

 such as nagana, surra, dourine, etc. This 

 condition of active immunity is seemingly 

 possible only in those species of animals 

 that are relatively insusceptible, for with 

 really susceptible species the infection is 

 always fatal. 



Heretofore all experiments on artificial 

 immunity against trypanosomes have been 

 made on animals that have recovered from 

 the effects of the parasite which has been 

 living and multiplying in the blood-vessels 

 of that animal. Now that cultures of some 

 of these organisms, as for example T. 

 leivisi of the rat and T. irucei of nagana, 

 are possible it was desirable to ascertain 

 whether or not they could be used to im- 

 munize against the virulent organisms. It 

 may be said, in passing, that cultures of 

 both of these trypanosomes, even after they 

 have passed through a hundred generations 

 or subcultures in the course of two years, 

 do not become attenuated by such pro- 



