THE THYMUS GLAND 121 



EFFECTS OF THYMUS EXTRACT. 



Svehla (1896) found that the watery extract of the thymus of 

 man and of certain animals (pig, dog, ox), when injected into the 

 veins of dogs, produces an acceleration of the pulse and a re- 

 duction of arterial tension. The fall in pressure is the expression 

 of an enfeebling, or of a paralysis, of the vasoconstrictors, while the 

 acceleration of the heart's action is the result of the direct influence 

 of the extract upon the cardiac muscles themselves, and not upon 

 the nervous apparatus which accelerates cardiac activity. The 

 arrest of respiration and of cardiac activity which sometimes 

 follow large closes of thymus extract, are secondary results of the 

 peripheral vaso-motor paralysis. 



Svelha showed further that this specific substance is not pre- 

 sent in the thymus of the human embryo, but is formed after 

 birth. Its activity apparently becomes stronger with time and, 

 even at the age of 40, the thymus in man still retains its specific 

 activity. Both the toxicity of thymus extract and its influence in 

 reducing pressure have been confirmed by other investigators 

 (Basch, Livon, Vincent and Sheen). Vincent and Sheen, how- 

 ever, emphasize the fact that substances with similar depressant 

 effects are obtained from many tissues besides the thymus. Farini 

 and Vedoni also describe the depressant action of thymus extract ; 

 they found that blood containing thymus extract, when circulated 

 by artificial means through the hinder extremities, did not produce 

 a vaso-dilation, but a vaso-contraction, which lasted, however, 

 only a short time. R. Popper (1905) discovered that the marked 

 reduction of blood-pressure which, together with suffocation and 

 heart failure, follows the intravenous injection of homologous 

 thymus extract, is not the result of a specific toxic activity of the 

 thymus extract upon the circulatory apparatus, but is due to a 

 property common to all tissue extracts, that, namely" of producing 

 intravascular coagulation and so giving rise to circulatory disturb- 

 ances. He found that, in rabbits which died after the injection 

 of thymus extract, there were extensive areas of coagulation in 

 the vascular system and in the heart ; dogs, however, usually re- 

 covered, the formation of thrombi being confined to single vessels. 

 If the coagulation of the blood is prevented by means of extract 

 of leeches, the action of the thymus extract ceases to be toxic, and 

 the reduction in blood-pressure appears only after very large 

 doses, and then in a very slight degree. 



Thymus extract remains active after boiling, and this shows 

 that its active principle is not, in itself, a ferment, but that it is a 

 substance which causes the formation of a ferment having the 

 property of coagulating blood. 



