In another gallery we may examine the evolution of the nerve system from the lowest to the highest. At the end of the series are placed the massive and complex brains of various races of mankind; much further down the series we note the small and simple brain of the marmoset. In shape it is not unlike the brain of the human foetus at the end of the third month of development. We note that the brains of the great anthropoids in size and complexity are intermediate to the comparatively simple brain of the gibbon on the one hand and the human brain on the other. One point rather impresses us. As far as the skeleton was concerned we saw that the gibbon and the monkey were widely separated, but when we come to examine their brains the difference between them appears to be much less in degree. Yet in every point in which the brain of the gibbon departs from that of the monkey it approaches the cerebral forms of the great anthropoids.
We might examine each system of the human body in turn, but it is unnecessary, for the anatomical evidence to be thus obtained would but bear out what we have already gathered. We see that man is a member of that group of mammals we have named the higher primates. He is one of the three families included in that group. The central family is represented by the great anthropoids ; man on the one side and the gibbon on the other represent the two other families. All three families we believe to have arisen from a common ancestral stock, but while the gibbon has clung to the ancestral form, man has progressively and aberrantly evolved to his present position.
The great anthropoids have been steered in a middle course, and will without doubt at no distant date be extinguished when European civilization reaches their jungle homes. Then will there be a wide gap between man and his nearest living allies.
Of late years we have obtained evidence of another character which throws a strange light on the close relationship which exists between man and the great anthropoids. We have been in the habit of thinking that many diseases were peculiar to man, and that no other animal could be infected with them. Such, for example, was believed to be the case in syphilis. If an ordinary monkey is infected with this disease, no real inoculation takes place ; at the most only a passing disturbance is manifested. The chimpanzee and orang can be really infected, as has been proved by those who are seeking to find a remedy for a disease which often produces most disastrous effects on man. The great anthropoids suffer only from the milder effects of the disease. Yet we have proof here that the constitutions of the great anthropoids have much in common with that of man, which is comprehensible if both are descendants of a common stock. Professor Grunbaum has shown that the anthropoids are also susceptible to other human infectious diseases. Bacteriologists have thrown a flood of light on the constitutional nature of animals.
In the course of their researches a method was discovered by which a minute quantity of the blood of any animal can be detected. The manner in which the test is carried out is highly technical. A special solution is prepared for testing the blood of each animal. We shall suppose that the solution prepared is for detecting human blood. When to this solution is added a fluid in which a stain of human blood has been dissolved a cloudiness appears in the solution, and a precipitate occurs in the test-tube. No other blood except human will give the full precipitate. If a solution of dog's blood is added there is no result. Professor Nuttall found, however, that a precipitate could be obtained with the blood of anthropoids—not so plentifully as is the case with human blood, but yet enough to show that in " blood relationship " man and the anthropoids stand very near together.