THE PAKATHYKOID GLANDS 525 



removal of the parathyroid glands. If the latest theory advanced by 

 Paton is correct, viz., that the symptoms of tetany are due to the accumu- 

 lation of guanidin or some allied substance which follows suppression of 

 the parathyroid function, it is quite conceivable that in certain classes of 

 animals, and under certain conditions, this poison might not be produced 

 in sufficient quantity to cause harm, or that the bodily mechanism might 

 quickly adapt itself to the altered conditions, so as to bring about its de- 

 struction by some agent other than the vital activity of the parathyroid 

 glands. Until we have more exact information concerning the role played 

 by the parathyroids, it is premature to assert positively that in all mam- 

 mals they are essential to life, and that, if, after their attempted re- 

 moval, postoperative tetany does not supervene, the absence of acute symp- 

 toms is due to the fact that some parathyroid tissue has been left behind, 

 although the most careful search may fail to reveal any. 



Accessory Factors in the Results of Parathyroidectomy. Effects of 

 Age on the Results of Parathyroid Extirpation. As already mentioned 

 incidentally, one factor which appears to influence the effects of parathy- 

 roid extirpation is the age of the animal employed. Raynard stated as 

 early as 1834 that this is so in dogs. Horsley (&) in 1886 called attention 

 to the influence of age on the results following what he at that time believed 

 to be simple thyroidectomy, but what was in reality in the carnivora thyro- 

 parathyroidectomy. He says: "I find that the determining factor, par 

 excellence, of the value of the gland as regards its influence on the general 

 metabolic processes of the animal is age. The effect of removing the gland 

 in the young animal is the rapid appearance of violent nervous symptoms 

 and death in a few days ; in a rather older animal, e.g., a one year old dog, 

 the symptoms are less violent, later in their appearance, and the animal 

 survives perhaps for a fortnight or three weeks ; in a very old animal the 

 removal of the gland simply hastens the torpor of old age; these observa- 

 tions refer to cats and dogs." 



Ewald also observed that the symptoms in aged dogs were usually 

 slight. 



MacCallum, Thomson, and Murphy (1907) performed thyroparathy- 

 roidectomy in eight goats and five sheep. The sheep were adults and prac- 

 tically no effect was produced on them, and in the goats the most definite 

 results were obtained in the very young. a We do not know how to explain 

 satisfactorily the negative results in so many of these animals, unless it 

 be that, in spite of our extremely careful and conscientious search," both 

 before and after death, "there are still other masses of parathyroid tissue 

 hidden away somewhere in the neck or thorax. It does not seem reasonable 

 to suppose that organs, which are so clearly shown to have a special function 

 in carnivorous and most other animals, should be highly developed in the 

 herbivora and still have no special functional importance." This shows 



