DISCUSSION ON ANIMAL TISSUE RESPIRATION 269 



The Muscle Strip Technique.— In most experiments reported in 

 the literature where skeletal muscle has been employed, it has either 

 been minced or chopped with scissors if larger animals have been 

 used, or the diaphragm of a small animal, such as the rat, has been 

 employed intact. The chopping or mincing is extremely destructive, 

 sets up abnormal chemical processes in the presence of oxygen, such 

 as aerobic glycolysis, and permits brief survival. The rat diaphragm, 

 while excellent for many purposes, is small, permits of few con- 

 comitant chemical measurements, and has only a limited usefulness 

 because of the fact that many metabolic conditions, such as diabetes, 

 cannot be brought about in this animal. The dog is a much better 

 experimental animal in these respects. The neck muscles of the dog 

 are ideal for obtaining, by careful dissection, long muscle strips for 

 in vitro studies. Individual fibers can be teased out intact. These 

 maintain their histological integrity for long periods. They respond 

 to electrical stimulation for hours unchanged, and give reproducible 

 results as far as work and heat production. Furthermore, enough 

 material can be obtained to allow for extensive chemical balances. 

 It is, I am sure, the method to be used when this type of tissue is 

 employed with in vitro studies. 



Minced Tissue.— Here the choice lies between using a Latapie 

 mincer or a homogenizing apparatus described by Potter. Histo- 

 logical examination of the tissue obtained by these two methods 

 shows that with the homogenizer the tissue is completely and uni- 

 formly disintegrated, whereas with the Latapie the destruction is 

 not complete and the tissue is a mixture of disintegrated and intact 

 cells. The amount of destruction differs with the organ, and these 

 differences are paralleled by differences in the rate of respiration. 

 For example, skeletal muscle because of its long fiber is completely 

 destroyed by both methods and the rate of respiration is the same. 

 With the parenchymatous organs, such as the liver and kidney, a 

 definite difference in respiration results from the two methods, the 

 respiration of the homogenized tissue being lower than that of the 

 Latapie. The same is true of cardiac muscle. The higher respiration 

 may be due to the presence of the intact cells in the tissue put 

 through the Latapie. Obviously tissues minced by these two methods 

 are not comparable with respect to respiration, and other differences 

 may exist. This discrepancy should be borne in mind whenever the 

 two methods yield different results. It would certainly seem desir- 

 able to decide on one or the other. My preference would be homog- 



