i INTERNAL PEOTECTIVE SECRETIONS 21 



tion of one thyroid only was innocuous in the dog. On the other 

 hand, he found that if the thyroid of one dog were grafted into 

 the peritoneal cavity of another, and the two thyroids of the latter 

 extirpated after a considerable period, the pathological phenomena 

 were delayed, and the animal survived the operation longer. He 

 observed that, generally speaking, the grafted thyroid did not take 

 root, but was absorbed after a certain time. He explained the 

 protracted survival of the animals on the assumption that during 

 the disintegration of the thyroid introduced into the peritoneum, 

 the substances necessary to the normal nutrition of the nervous 

 system are absorbed and carried to the circulation. He con- 

 jectured that the same effect could be obtained by the periodic 

 injection of thyroid juice into a dethyroidised animal, as was 

 subsequently demonstrated by other experimenters. 



Another important fact stands out in Schiffs memoir. He 

 states that if both thyroids in a dog are excised in two successive 

 operations, at about a month's interval, no pathological symptoms 

 appear in the animal. With a less interval between the two 

 operations, the fatal symptoms are delayed; if the interval is 

 reduced to one week they invariably set in. This suggested to 

 Schiff the hypothesis that in the interval between the first and 

 second thyroidectomy the activity of another organ, similar to or 

 identical in function with the thyroid, might be progressively 

 exaggerated, so as to act vicariously for the excised thyroid. The 

 presumptive existence of another organ functioning vicariously for 

 the thyroid, explains, he says, why total thyroidectomy in certain 

 animals, e.g. rabbits and rats, and on rare occasions dogs also, may 

 be innocuous. Later on we shall examine the value of this 

 hypothesis. Meantime it may be stated that the fundamental 

 fact on which it is based was immediately contradicted by the 

 experiments of Sanquirico and Canalis (1884-85), who constantly 

 obtained fatal results from the removal in two operations of both 

 thyroids in dogs, whatever the period between the first and second 

 operation. They also observed another enigmatical fact, the 

 importance of which will appear below. Eemoval of the upper half 

 of both thyroids is fatal in the dog, while removal of the two 

 lower halves is innocuous. 



Immediately after Schiff' s publication, Colzi proposed that 

 these experiments upon the thyroid should be repeated in our 

 laboratory in Florence, in order to see, from an exclusively 

 surgical standpoint, which minimal portion of the organ it was 

 necessary to preserve in dogs in order to avoid the phenomena of 

 " tetania thyreopriva." The results of his experiments, published in 

 1884, showed that if half the thyroid, or even half of one lobe 

 were retained, the animal escaped death. In this case transitory 

 phenomena of functional insufficiency were often apparent. 



The rapid course and violence of the phenomena of tetany as 



