XL THE ROYAL SOCIETY OF CANADA 
also the serum to be tested, which can be much diluted in salt-solution. 
A definite quantity of fresh serum from a guinea-pig is added, and if 
the two former are homologous (that is, if in the present instance the 
serum to be tested is human), then precipitation will take place and 
complement will be deviated from the fresh serum. The disappearance 
of the latter is shown by the addition of a “hæmolytic system” con- 
sisting of washed sheep blood-corpuscles and inactivated rabbit-anti- 
sheep serum. If the complement has disappeared, then the blood 
corpuscles will not be dissolved, but if there is still free complement, 
hemolysis will take place, furnishing a proof that the sera were not 
completely homologous. Dr. Bruck made a series of experiments of 
this nature in Java regarding the blood-relationship of Man and the 
other primates, and found that with human serum diluted one in two 
thousand complete hemolysis took place. It did not occur with a 
solution of one in a thousand, showing that all the complement had 
disappeared. On the other hand, the blood of the Orang-utan tested 
by the same anti-human serum showed the absence of complete ho- 
mology by the existence of free complement even in a solution of one 
in two hundred. His experiments indicated that by this test the 
Orang-utan is as far removed from Man in one direction as it is from 
the Rhesus monkey in the other. Bruck further thought that he could 
distinguish in this way between the blood of different races of Man 
in Java; but his experiments have not been confirmed by other ob- 
servers. 
A remarkable proof of the specific peculiarities of the blood of 
each species of animal has been recently furnished by Reichert and 
Brown. Unlike most of the albuminous substances of the body, the 
colouring matter of the blood forms distinct blood-crystals. These 
have been studied by the methods adopted by mineralogists in the 
examination of ordinary crystals, and the result of the crystallographic 
study is that each species has a characteristic crystalline form for its 
hemoglobin and that related species have crystals which merely fall 
into the same system. It has been possible to show by this method, 
for example, that the dog and the wolf are more nearly related to each 
other than are the cat and the lynx; that the fur-seals are more nearly 
related to the bears, the harbour-seals to the otters, the polyphyletic 
character of the Pinnipedia being thus indicated. 
PROTOZOOLOGY. 
These references to the blood remind one that bacteria are not 
alone in producing formidable diseases. There are also some humble 
forms of animal life, the knowledge of which has been entirely acquired 
in the period I am dealing with, which are responsible for malaria and 
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