88 NATURE-STUDY REVIEW [13:3— Mar., 1917 



The white rat is an albino. Over in west-central Africa there 

 is a race of men, of negro extraction, whose hair and skins are white 

 and whose eyes are of deep pink color. Long ago the Portuguese, 

 observing these people, called them albinos, a name referring to 

 their white color. We now know that albinism is a common 

 occurrence in both the plant and animal kingdoms. By isolating 

 albino individuals and breeding them together we may obtain 

 albino races. Thus have arisen white blackberries, white rasp- 

 berries, white currants and white strawberries. Albino races 

 among animals are even more numerous ; we have them in rabbi cs, 

 mice, rats, guinea-pigs, sheep, goats, cattle, dogs, cats, horses 

 and many others. 



Albinism is due to the absence of pigment or coloring matter 

 in tissues that normally possess them — in skin, hair and eyes, 

 for example. Just what causes some individuals of a species 

 to lack pigment, and other individuals to possess it, we do not 

 fully understand The Laboratory for Experimental Evolution, 

 maintained by the Carnegie Institution at Cold Spring Harbor, 

 L. I., is working on this problem at the present time and hopes 

 to solve it shortly. Its workers have already arrived at a partial 

 solution. They tell us that there is a correlation between new 

 cases of albinism and consanguinity, and that albinos, when 

 mated together, always produce albinos. Albino rats, for instance, 

 mating with each other, produce albino young only. When an 

 albino rat mates with a black or brown rat, however, it produces 

 both albinos and blacks or browns, in the proportion of about 

 half albinos and half blacks or browns. 



The white rat shown in the views had pink eyes, a character 

 possessed by most albinos. The cause of this color is very simple, 

 although a mystery to most persons. The iris and retina of eyes 

 are richly supplied with blood vessels. Now, in normal eyes, 

 these blood vessels are concealed by pigment and so are never 

 seen, but in albino eyes, which lack this pigment, they are exposed 

 to view, and give the eyes a deep-pink color. We are looking at 

 a complex web of minute blood tubes when we look at a white 

 rat's eye. 



Pink eyes have advantages and disadvantages. In sunlight, 

 they are easily blinded, due to their transparency and inability 

 to withstand bright rays of light. But at night time they more 

 than make up for this deficiency; then they become powerful, 



