STUDIES IN THE REGENERATION OF BLOOD 243 



scissors, and the animal held over a weighed glass vessel into which the 

 blood was allowed to drop. If care was exercised it trickled slowly and 

 in a well-directed stream and scarcely touched the fur. The blood was 

 allowed to flow into the dish up to the mark previously placed to indicate 

 one-third the estimated total volume of blood. By the time this had 

 run out a clot had usually formed. The clot was carefully and gently 

 wiped off from the wound with a previously weighed bit of cotton, and 

 this added to the blood in the dish, and the whole was then weighed. 

 If a clot failed to form the bleeding was stopped by pressing a small 

 (weighed) piece of cotton against the cut in the Vein. Ordinarily this 

 proved effective. If less than one-third of the (estimated) rat's blood 

 had run out by the time a clot had formed, it was easy to start the 

 bleeding again by harshly wiping the nick in the vein with a weighed 

 pledget of cotton; then more blood dripped and a second weighing 

 was made. This second bleeding was, however, seldom necessary. 

 The wound in the skin was then washed with dilute alcohol (25 per 

 cent) and sewed up. The rats recovered readily, the wound healing 

 in from 2 to 3 days in every case. 



Blood counts and hemoglobin determinations were made daily until 

 the original values returned. During the period of regeneration frag- 

 mentary red cells were often seen in the blood, but as regeneration 

 proceeded these became fewer in number and finally disappeared alto- 

 gether. The number of leucocytes increased the first day or two after 

 the hemorrhage, but not in great abundance. As shown by Lamson (7) 

 the number of erythrocytes as well as the percentage of hemoglobin 

 varies among the individuals, but the drop after hemorrhage in each 

 case is comparable. 



Criteria of regeneration. The return of the number of red blood cor- 

 puscles and the percentage of hemoglobin to the values noted before any 

 loss of blood had been sustained by the rat were the criteria used in 

 judging regeneration. These values remained approximately constant 

 for two successive days before the rat was considered to have regenerated 

 his blood. For normal animals of either sex fed on standard diet 

 (see footnote 2) with the addition of dried brewery yeast, the time was 

 from 6 to 9 days (table 1). This has been corroborated by the sub- 

 sequent studies of Geiling and Green (8) in this laboratory. At the 

 end of the period required for regeneration, in many cases a second 

 hemorrhage required about the same time for a return to normal blood 

 conditions. A third hemorrhage "was made on some of these rats, but 

 regeneration in such animals always needed more time. If, however, 



