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pretation of this — that these substances in the blood capable of 

 liquefying blood cells cannot get into the cells, and so cannot 

 liquefy them, but they can penetrate the cells of foreign species 

 of animals and so liquefy them. In fertilization the liquefaction 

 of the fertilized cell is incomplete. Only sufficient liquefaction 

 of a cell takes place to cause the formation of the clear membrane 

 on the outside, and the result is that the cell behaves as if it 

 has been fertilized, and goes straight ahead with its development. 

 It has been pointed out long ago that the cells of tumors or of 

 cancers behave very much as if they were sex cells which have 

 become fertilized. They bear a very strong analogy to a 



fertilized egg cell. A sudden explosion of energy takes place. A 

 tremendous structure is built up out of a single cell. A cancer 

 cell starts dividing and goes on ad infinitum. What causes this 

 sudden awakening of a cell Avhich apparently had reached its 

 maximum development and become quiescent, and stopped 

 dividing P Some light is thrown on this question by the above 

 results. 



A striking analogy to these experiments of Professor Jacques 

 Loeb is provided by some experiments of his brother, Professor 

 Leo Loeb of the University of Pennsylvania, Philadelphia. The 

 latter is considered the leading authority on cancer in the United 

 States. One of the most remarkable phenomena accompanying 

 the formation of an embryo in mammalia, to which class of animals 

 we belong, is the growth from the tissues of the uterus of a struc- 

 ture designed to supply the growing embryo with blood — the 

 placenta. The growth of this structure may not inaptly be com- 

 pared with that of cancer or tumor. There is a sudden liberation 

 of energy among the cells of the uterus. The cells start dividing, 

 and produce a large quantity of tissue. Prof. Leo Loeb has 

 made the following discovery. He took virgin guinea pigs and, 

 at various periods of their lives, made incisions in the uterus. 

 Ordinarily nothing resulted, but, during a certain brief period, 

 from four to nine days following the period of heat, typical placen- 

 tas were produced. Any injury to the uterus at that stage pro- 

 duced a placenta. If he took the blood of guinea pigs in that stage 

 and circulated it in the blood of another guinea pig not at 

 that stage any incision whatever in the uterus of the second 

 guinea pig produced a placenta. In other words, some substance 

 was present in the blood of the guinea pig at that moment which 

 rendered the cells of the uterus sensitive. That sensitiveness of 

 the uterus at that critical . period is obviously connected with the 

 presence in the blood of some secretion from the ovaries, because 

 if the ovaries were removed no such effect was observed, and it 

 was never possible to get a placenta in any guinea pig deprived 

 of its ovaries. Evidently the presence in the blood of that sub- 

 stance derived from the ovaries only occurs during the period 

 following the period of heat. If it were continuous we should 

 get, not the growth of a temporary placenta, but a permanent 

 and continuously increasing growth — in other words, a cancer. 

 That is to say, if sensitizing substances be present in the blood, 

 cells which are injured in the body or receive certain excitations 

 in the body, are very likely to start development, as if they had 

 been fertilized, and to produce abnormal growths. I think you 

 will agree with me that this is a rather striking analogy to the 

 fact that we cannot fertilize, ordinarily, the eggs of the sea-urchin 

 with foreign blood, but we can readily do so if we sensitize them 

 first with special substances. What is believed to take place when 



