THE BLOOD. 173 



made, 1 it being usually stated that its weight constitutes one-fifth of 

 that of the whole body. Ed. Weber has, however, recently insti- 

 tuted some experiments, according to which only one-eighth of the 

 weight of the body is blood, or 18 pounds for a man weighing 144 

 pounds. Lehmann calculates that the whole amount of blood in a 

 young man is 17J to 19 pounds. The estimate of Weber appears 

 to be the most accurate hitherto made. It is calculated that only 

 one-third of the whole blood can be lost rapidly without fatal con- 

 sequences. But much more than this may be ultimately lost by 

 frequently recurring hemorrhages, the vessels thus having time to 

 adapt themselves to the diminished amount of their contents, so 

 that the circulation is still maintained. 



Varieties in the Composition of the Blood in different Physiological 



Conditions. 



1. Sexual varieties. The blood of women is of a lighter red color 

 than that of men. is specifically lighter, contains more water, and 

 evolves a less intense odor of perspiration when treated witn 1J 

 times its volume of sulphuric acid. It generally contains less cor- 

 puscles, but the same amount of fibrine (Lehmann) ; and some more 

 serum in proportion to the clot. It usually contains more albumen 

 and salts (especially the soluble), and less fat and extractive matters. 



2. In pregnancy the blood is darker than usually, is richer in 

 water and poorer in corpuscles and albumen, and therefore speci- 

 fically lighter. There are no certain data respecting the fats and 

 salts ; but the fibrine is relatively increased in the last months, and 

 the clot is generally very small, with a superficial stratum of fibrine 

 frequently resting upon it (p. 158). 



3. Varieties depending on age. The blood of new-born infants 

 abounds in solid constituents, especially blood-corpuscles and iron, 

 while it is poor in fibrine and salts. It contains about the same 

 amount of fat and albumen as in the adult, and a much larger pro- 

 portion of extractive matters. In advanced life, and in the female 

 after the cessation of the catamenia, the blood is poorer in corpuscles, 

 and the serum loses in some of its constituents, but the cholesterine 

 increases. 



4. During digestion, both the plasma and the cells become richer 

 in solid constituents ; though the latter experience a relative loss 



1 Blumenbach estimates it at 8 to 10 pounds ; Reil at even 44 pounds. 



