34 PHYSIOLOGY CHAP. 



injections, besides suspending the phenomena of tetany, effected 

 a sensible prolongation of the life of the animal. Lusena added 

 the further fact that injections of pure thyroid juice exerted no 

 beneficial influence on the syndrome of parathyroidectoiny or 

 thyro-parathyroidectoniy, and that the injection of the juice 

 prepared from the thyroids of dogs that had tetany from para- 

 thyroidectoiny, aggravated the symptoms of thyro-parathyroid- 

 ectomy. This last result rests on a single experiment only, and 

 deserves to be confirmed by further research. 



Lastly, Lusena has established by the method of reciprocal 

 transfusion, or that of the partial substitution of the blood by an 

 isotonic solution of sodium chloride, that the phenomena of tetany 

 in parathyroidectomy can be suspended or attenuated like those 

 of thyro-parathyroidectomy. In the first as in the second case, 

 accordingly, there must be toxic substances in the blood of the 

 animals that have been operated on. 



All these interesting data as to the functional importance of 

 the parathyroids throw new light upon many obscure points, and 

 subtract not a little from the value of the earlier conclusions as 

 to the physiology of the thyro-parathyroid system. 



We can now see why rabbits and other animals frequently 

 survive complete extirpation of the thyroids, and why even dogs, 

 on which the greatest number of experiments have been carried 

 out with positive results^ may also survive. This is evidently 

 due to the fact that the external parathyroids are constantly in 

 rabbits, and occasionally in dogs, distinct from the thyroid lobes, 

 and are therefore left in situ when those lobes are excised. 



So, too, we can explain why, after excision of goitre, the patient 

 may only exhibit symptoms of a slowly progressing cachexia 

 thyreopriva or operative myxoedenia, while in other less frequent 

 cases acute phenomena of tetany supervene. Previous to the 

 investigation of the parathyroids, these two essentially distinct 

 pathological forms were regarded as different steps of one identical 

 process, due to the abolition of the function of a single gland, 

 the thyroid. Cachexia thyreopriva is now held to be the effect of 

 functional deficiency of the thyroid gland alone, and tetany the 

 effect of inhibited function of the parathyroids. In excision of 

 goitre by the subcapsular method, the surgeon in the majority of 

 cases leaves the inferior parathyroids, which are distinct from 

 the thyroid lobes ; but in certain cases the inferior parathyroids 

 are included in the ablation of the thyroid, being joined to the 

 body of it. In the first case cachexia ensues, in the second tetany. 

 Sometimes there may be transitory or intermittent tetany, in 

 consequence of functional insufficiency of the parathyroids. This 

 occurs, according to Yassale, when a single inferior parathyroid 

 is left in situ during the operation. In order to avert this 

 pathological consequence, it is necessary for the operator to spare 



