6 LECTURE I. 



find, first of all, that it is indirect in character. Here we meet with the most 

 remarkable point in all physiological-chemical investigation. A very 

 large part of it is based upon indirect proofs. Its inadequacy is clearly 

 shown if we choose for illustration, instead of the above very transparent 

 example, something more complicated, such as, for example, the question 

 now in the foreground of general interest with regard to the formation of 

 sugar from other sources than carbohydrates. By extirpating the pan- 

 creatic gland of a dog, its carbohydrate metabolism may be so disturbed 

 that sugar is constantly eliminated in the urine, and one would naturally 

 think a priori that in such a case it would be possible to determine with- 

 out difficulty whether, for example, albumin or fat can cause secretion of 

 sugar in the urine. As a matter of fact, this secretion of sugar continues 

 even after all carbohydrates are completely eliminated from the nourish- 

 ment. We may assume this to prove that albumin and fat can cause 

 secretion of sugar in the urine. Although we are justified in drawing such 

 a conclusion, it is not necessarily a correct one. A result from a given 

 experiment can lead to different conclusions according to the standpoint 

 assumed by the individual investigator. In this case it is possible to 

 explain the continued secretion of sugar in another way. The animal 

 organism possesses constant reserves. Their extent has only recently 

 been realized. From them, and especially from carbohydrate stores, the 

 sugar may have its source. The conclusion that the animal cell is capa- 

 ble of forming sugar from other sources than the carbohydrates can only 

 be drawn with certainty after it has been established that the organism 

 has no more carbohydrates at its disposal. Not till this has been clearly 

 shown will the above conclusion rest upon a firm basis. It remains still 

 undecided, even if the carbohydrates as sugar-formers are fortunately 

 excluded, as to whether fats and albumins belong to this class of com- 

 pounds. Now it has been often observed that in feeding albumin to a dog 

 with no pancreas the elimination of nitrogen runs practically parallel 

 to that of sugar. This repeatedly established relation between the break- 

 ing down of albumin and the formation of sugar has been given as a direct 

 proof for the formation of sugar from albumin, and in fact one might 

 be tempted to assume that this is actually a direct demonstration. 

 E. Pfliiger, whom we have to thank for a detailed critical review of all the 

 work in this field, is of an altogether different opinion. If we assume as 

 correct that the elimination of sugar and of nitrogen increases at an equal 

 rate, we are still far from being justified in assuming that the increase in 

 sugar is directly due to the breaking down of the albumin which is taking 

 place. The cells of a dog with no pancreas, and those of a diabetic, have 

 not lost entirely the power of consuming sugar, and in all cases a part of 

 the sugar formed is burned up. If now albumin be fed, it will also be 

 burned; in other words, there will be set free in the tissues of the organism 



