REGULATION OF ENVIRONMENT 81 



ered. The capillary walls seem to take up the liquid 

 and solid material required, and this material is at the 

 same time reconstituted so as to produce blood plasma 

 of normal composition. But the regeneration of the 

 lost red corpuscles is a much slower process, so that the 

 new blood is at first very deficient in corpuscles, and 

 several weeks may be needed for their complete regen- 

 eration. If, however, the bleeding is repeated at inter- 

 vals the process of regeneration of corpuscles becomes 

 faster and faster, so that frequent re-bleedings can 

 be easily borne by the animal. Similarly, if blood is 

 transfused from one animal to another the liquid part 

 of the injected blood is rapidly eliminated, but not the 

 red corpuscles. Hence for a considerable time the 

 blood is abnormally rich in corpuscles. If, however, 

 the transfusion is several times repeated the excess of 

 corpuscles disappears more and more rapidly. The 

 capacity of both the blood-forming and the blood-de- 

 stroying process is thus increased by use. Young red 

 corpuscles are known to be formed in the bone-mar- 

 row, while the products of destruction of red cor- 

 puscles are found in the liver and excreted in the bile. 

 The capacity for formation or destruction of corpus- 

 cles is thus associated with the physiological activity 

 of these parts of the body, but this activity is evidently 

 regulated with great exactitude. 



If we look, not merely at the internal, but also at the 

 external activities of an organism Claude Bernard's 

 generalisation seems still to hold. The co-ordinated 

 activities of the senses and muscular system are mainly 

 directed to the end of providing for nutrition. Behind 



