AMOUNT OF BLOOD EXISTING IN ANIMALS. 



21 



If, however, the experiment be carefully performed, without allowing any loss 

 of blood, or too great a length of time to elapse between the injection of the water 

 and the abstraction of the second portion of blood, results approaching very nearly 

 to the truth may be obtained. 



Another method has been suggested, dependent for its accuracy upon the fact 

 that iron exists only in the blood-corpuscles and hair, and consequently when the 

 latter is shaved off, it will be found only in the former. 



A definite portion of blood is abstracted, and the proportion of iron determined. 

 The whole animal is then burned, the ashes collected, and the amount of iron 

 ascertained. By a comparison of this with the amount existing in a definite quan- 

 tity of blood, the whole amount of blood may be determined. This method, if 

 practicable, promises accurate results. 



Another method, proposed by Lehmann,^ is founded upon the fact that only a 

 definite amount of grape sugar can exist in the blood at any one time, without its 

 elimination by the kidneys. 



Having ascertained how much grape sugar the blood m.ay normally contain 

 under favorable circumstances, the quantity of blood contained in an animal may 

 be calculated by ascertaining the quantity of sugar which must be introduced into 

 the circulatory fluid in order to make it pass into the urine. 



The methods of Valentin and Lehmann might be applicable to warm-blooded 

 animals, whose circulation is rapid, and whose excretions and secretions are corre- 

 spondingly abundant. They are, however, wholly inapplicable to cold-blooded 

 animals. 



In the first place, the circulation in this class is sluggish, and the blood, owing to 

 the peculiarities of the structure of the circulatory apparatus, is not diffused uni- 

 formly to all the organs and tissues, as in the higher animals. In the second 

 place, the secretions and excretions are exceedingly slow, and small in amount. 

 Many animals of this class do not void their urine more than once in a month 

 during starvation, and then in exceedingly small quantities. In many the bladder 

 is absent, and where it does exist, even supposing that the urine was rapidly 

 excreted, owing to the structure and position of the urinary apparatus, it is next 

 to impossible to draw off the contents of the bladder. 



From these considerations, then, it would be utterly impossible to determine the 

 amount of blood in cold-blooded animals, by injecting into the circulatory system 

 either water or grape sugar. 



The method, also, of determining the quantity of blood from the relative pro- 

 portion of iron in a definite amount of blood and in the ash of the whole body, 

 would also, in many animals of this class, be absolutely impossible. The Chelonians. 



' Lelimann's Physiological Chemistry, translated by G. E. Day, Amer. edit., Philad., 1855, I, 639. 



Other methods of determining the amount of blood have been proposed, but not practised, by the 

 following physiologists: Vogel, Pathol. Anat. dcs nicnchl. Korpers, Leipz., 1845, s. 59 (or English 

 translation, p. 84). Dumas, Chim. Pliysiol. et Med., Paris, 1848, p. 326. Weisz, Zeitsch. d. k. li. 

 Gesellsch. d. Aertze, Dec. ISlt, s. 203-229. 



