FORMATION OF BLOOD-CELLS. 101 



young chicken is effected ; but the change can not take place except ox- 

 ygen be received through the shell ; and, indeed, in all cases in which al- 

 bumen passes into fibrin, it does so only in the presence of oxygen. 



But in the case of the absorbent glands, from what source does the 

 requisite oxygen come ? These glands have just been de- Manner in 

 scribed as plexuses of the absorbent tubes, among the rami- y hich oxygen 

 fications of which arteries and veins are abundantly distrib- the making of 

 uted, the blood not getting access to the interior of the ab- fibrin * 

 sorbent, but running in its own vessels, as it were, side by side, and 

 branching on the naked walls of the plexus ; and, just as in the placen- 

 tal circulation the arterial blood of the mother vivifies or furnishes oxy- 

 gen to the foatal blood, so in this instance the arterial blood enables the 

 cells to discharge their duty of converting the albumen into fibrin, which 

 passes onward to the general circulation for the renovation of the muscu- 

 lar tissues. 



Since the hourly consumption of fibrin may be taken at 62 grains, 

 the quantity produced by the action of these cells must be the same. 

 We may therefore affirm that the fibrin-producing mechanism yields 

 aboutjone grain in each minute of time. 



Contemporaneously with the elaboration of fibrin is the develop- 

 ment of the proper chyle corpuscles. Through the evolution Formation of 

 of these and the absorption, of fat, the chyle vessels present a Wood-cells, 

 connection with the respiratory apparatus. 



If any weight is to be given to the views of Ascherson, the occurrence 

 of fat globules in the chyle is essential to these cellular productions. 

 He found that when globules of oil are placed in a solution of albumen, 

 they become coated over with a film of that substance in a coagulated 

 state, and hence was led to infer that this is the starting-point of cell pro- 

 duction generally. 



The chyle corpuscles are the embryos of the true red blood-cells, the 

 latter being derived from them by gradual development. As will appear 

 more in detail when we come to the description of the blood, in verte- 

 brated animals there are two distinct classes of red blood- Twosuccessive 

 cells, which appertain to distinct periods of life. The first, forms of biood- 

 which are found in man previously to the time of formation Cl 

 of the chyle and lymph, are nucleated, and have the power of reproduc- 

 tion by fissuring of the nucleus. 



But a distinct set gradually replaces the preceding. These cells have 

 no nucleus ; they are flattened, bi-concave, and in man circular. They 

 possess no power of reproduction either by fissuring or otherwise. Their 

 origin is from the chyle corpuscle, the granular interior of which clears 

 up, and is succeeded by a deep red tint. The transition from the first 

 to the second of these forms takes place at an early period, and may be 



