516 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



water and therefore richer in organic materials than the parenchy- 

 matous tissues, but the Proteins which they contain are of very abnor- 

 mal composition, a composition which is specific for each type of 

 sclerous tissue. They are incomplete proteins, containing certain 

 ammo-acid radicals in exceptional abundance, while others which 

 usually occur in proteins of cellular origin are lacking or present in 

 unusually small amounts. To manufacture one molecule of a protein 

 of this abnormal character several molecules of the ordinary types of 

 protein must be sacrificed, just as several buildings constructed of 

 wood, stone and brick must be sacrificed to obtain the materials 

 wherewith to construct a similar building entirely of stone or of brick. 

 Hence the drain upon the nutrient-level in the circulating fluids which 

 is brought about by the sclerous tissues is far more than proportionate 

 to their mass. 



We have seen that the administration of Growth-catalyzers must 

 favor the development of parenchymatous as opposed to sclerous 

 tissues. Corresponding with this view and with the views expressed 

 above concerning the origin of senescence, we find that the continuous 

 administration of Tethelin to mice, from the fifth week of age onward, 

 or even its intermittent administration for several brief periods, leads 

 to a remarkable prolongation of the average Duration of Life. Thus 

 the duration of life of normal white mice was found in the particular 

 stock employed to be 767 days for males and 719 days for females 

 within a probable error of somewhat less than one month. Males 

 which had received 4 mgm. of tethelin daily throughout their lives 

 attained an average age of 866 days before death, while females inter- 

 mittently receiving the same dosage attained an average age of 800 

 days. This would be equivalent to a prolongation of from ten to 

 fifteen years in the average duration of life in man. Pituitary (anterior 

 lobe) tissue, cholesterol, and lecithin alike failed to influence the 

 duration of life, the pituitary tissue on account no doubt of the small- 

 ness of the dosage of tethelin contained in the amount of the tissue 

 which it was practicable to administer, and cholesterol on account of 

 the secondary deleterious effects of the deposits of this substance 

 which accumulate in the tissues of animals receiving excessive amounts. 

 The absence of any effect, of the administrations upon the life-duration 

 of these various groups of animals rendered them additional "controls" 

 by reference to which the prolongation of life attained by the adminis- 

 tration of tethelin could be gauged. The average duration of life of 

 the tethelin-fed males was found to exceed the average life-duration 

 of the males of all other classes of animals investigated by one hundred 

 and three days, while the life-duration of the tethelin-fed females ex- 

 ceeded that of all other classes by one hundred and eight days. The 

 chance of both of these deviations from normality being "accidental" 

 was computed to be only 1 in 1 1,000. The prolongation of life in mice 

 by the continuous or frequent administration of relatively large doses 

 of tethelin is therefore unmistakable, Furthermore, Senescence is very 



