182 CIRCULATORY SYSTfiBT. 



into the natural products of the soil; it is, perhaps, most rea- 

 sonable to conclude that they are generated in the laboratory 

 of the animal system itself, by the all-controlling influence of 

 the living principle."* 



The red globules, according to the opinion of Mr. Hunter, 

 from not being pushed into the extreme arteries, where the 

 coagulating lymph reaches, and from not being found in all ani- 

 mals, do not contribute to the growth and to the repair of the 

 system. But they seem to be connected with strengthen such 

 animals as have them, as the strength acquired by exercise in- 

 creases their proportion and occasions them to be carried abun- 

 dantly into parts which previously, from a debilitated state, re- 

 ceived them but partially, if at all. This fact is well known to 

 graziers, who keep their quantity in certain animals, as veal, 

 reduced by quietude and frequent bleeding. 



Their source is not understood, though many conjectures on 

 the subject have been hazarded. Mr. Hunter's opinion was, 

 that they do not appear to be formed in those parts of the blood 

 already produced, but rather to rise up in the surrounding parts: 

 as, in the incubated egg, they exist in the form of a zone, com- 

 posed of dots, previously to the formation of vessels. This fact 

 ought to quiet all speculations about their coming from the spleen ? 

 thymus gland, and so on. 



* Good, loc. ciU 



