ON THE PHAGOCYTES OF THE ALIMENTARY CANAL, 488 
the kidneys almost as soon as they were formed. Moreover, 
Dr. Charrin and myself! have seen that the sterilised blood 
of a rabbit dying after the inoculation of the Bacillus 
pyocyaneus often contained enough vaccinating substance to 
vaccinate another rabbit, provided the sterilised extract of 
blood was injected into the second animal twenty-four hours 
before the Bacillus pyocyaneus was introduced. The first 
rabbit, though saturated with vaccinating substances, was 
unable to resist the attacks of the Bacillus pyocyaneus. 
The animal organism must not be compared to a cultivating 
medium which, after a particular kind of micro-organisms has 
grown in it for some time, contains substances having a harmful 
action on the micro-organisms producing them. The cells of 
an animal react against parasites; the kidneys excrete the poi- 
sons secreted by fungi in the diseased animal, for if the vac- 
cinating substances are thrown out of the animal body the 
poisons producing paralysis, fever, &c., have the same fate.? A 
living being is therefore provided with various means of 
defence against the invasion of microbes which are always 
threatening it. 
M. Metschnikoff’s investigations have undoubtedly thrown a 
new light on this question. He has shown that when patho- 
genic bacilli are inoculated into a vaccinated animal, or into 
an animal belonging to a species which successfully resists the 
attack of that particular kind of bacilli, some of the cells of 
these animals—cells to which he has given the name of macro- 
phages and microphages—fight against their hosts, swallow 
them up, destroy, and digest them. The observer’s eye on the 
microscope is able to follow the struggle for life in all its 
phases. 
M. Metschnikoff has also demonstrated the fact that, if an 
' Charrin and Armand Ruffer, ‘Compt. Rend. Soc. d. Biologie,’ March, 
1889. 
2 Bouchard, loc. cit.; Charrin and Armand Ruffer, ‘Comp. Rend. Soc. d. 
Biologie,’ 1889. 
3 Metschnikoff. The best account of M. Metschnikoff’s early researches will 
be found in ‘ Ann. de l'Institut Pasteur,’ No. 7, 1887. 
