HOW TISSUES ARE FREED FROM GLYCOGEN 325 



after being starved for several days or fed on flesh alone are 

 made to do excessive muscular work, immediately after which 

 they are killed and the tissues examined for glycogen. 



Certain poisons such as arsenic and phosphorus, which act 

 directly on the liver cells, and strychnine, which acts on the spinal 

 cord centres, producing general convulsions (i.e. excessive muscular 

 contractions) cause a considerable depression in the glycogen 

 deposits. 1 In the experimental diabetes caused by phlorhizin or 

 by extirpation of the pancreas the glycogen deposits, especially 

 those of the liver, become very much diminished in amount. We 

 shall have occasion to consider these points later on. 



WHAT FOOD-STUFFS LEAD TO GLYCOGEN FORMATION? 



This may be ascertained by seeing whether, by feeding an 

 animal rendered as nearly as possible glycogen-free, an accumu- 

 lation of glycogen is induced. This is the direct method. Its 

 results can be controlled by the indirect method. The rationale of 

 the latter is as follows. Since there can be no doubt that dextrose 

 forms glycogen the absolute proof of this will be considered 

 later any food- stuffs which during their metabolism yield dextrose 

 must also be glycogen formers. We can ascertain whether a food- 

 stuff yields dextrose during its metabolism by rendering an animal 

 incapable of oxidising carbohydrate in other words, by rendering 

 it diabetic and then seeing whether the food-stuff in question 

 causes an increase in the sugar excretion by the urine. If, for 

 example, we find that feeding a diabetic patient with proteid 



1 A very thorough method, depending on the use of strychnine, is that of 

 Frentzel ( 9 ). This worker showed that all traces of glycogen can be made to dis- 

 appear in rabbits by inducing strychnine convulsions for five hours after having 

 starved the animals for from one to two days. Previous to the starvation the 

 rabbits should be fed for some time on milk. During- the action of the 

 strychnine, artificial respiration is usually necessary, but care must of course be 

 taken that too large a dose of the drug is not given ; it should be such that the 

 convulsions are invoked only when the skin is irritated. After five hours the 

 strychnine is antidoted by chloral, so that the animals fall into a deep sleep. If 

 the animals be killed at any time up to twelve hours no glycogen will be found 

 in their liver or other tissues. After this time, however, glycogen begins to ap- 

 pear and steadily increases in amount. The source of this glycogen may be tissue 

 proteid. To study the influence of any food-stuff on the formation of glycogen 

 in the liver, the food-stuff in question should be given along with the chloral 

 and the animal killed in from ten to twelve hours. 



