I02 



NATURE 



[July 21, 192. 



cells off, the later growth of a tumour is due to the 

 division of its cells. As this growth proceeds, one of 

 two things happens. Either the tissues become pressed 

 upon and flattened out so that the tumour is said to 

 grow " expansively," or the tumour cells invade the 

 other tissues, gradually destroying them, and finally 

 insinuating or infiltrating themselves into lymph- 

 vessels or blood-vessels. Thus they may be swept 

 away and transported to the most remote ends of the 

 circulation, where, being arrested, they again start to 

 grow and produce a secondary or daughter tumour 

 which is a copy more or less perfect of the primary 

 growth. 



It is this last peculiarity which compels us to 

 place true tumours or blastomata in a class outside 

 the swellings caused by inflammatory processes, even 

 although the latter present a certain superficial re- 

 semblance to blastomata. The tumour cell itself is 

 or carries the actual exciting agent to continued cell 

 growth, and it is when we come to the question of the 

 cause of this extraordinary cell growth that we are in 

 Cimmerian darkness. We do not know whether there 

 is one or many causes of new growths, and our methods 

 of treatment, especially of the more autonomous or 

 malignant growths, are hopelessly defective. 



Theories of the Origin of Malignant Growths. 



Naturally, various causes of malignant growths have 

 been suggested, and three at least have been seriously 

 studied ; namely, irritation, the action of a parasite, 

 and embryonic aberration. 



(i) It is widely held that some irritation, physical 

 or chemical, applied over a long period may incite 

 the cells to unusual growth, which ultimately takes 

 an abnormal blastomatous course. In the last few 

 years, many experiments have concurred to show 

 that tar products may be active incitors to tumours 

 both in men and animals. Cancers in man are not 

 infrequently to be seen in association with some 

 chemical or infective irritation. 



(2) A second current of thought has centred round 

 the possibility that tumours, and especially cancers, 

 are due to an exogenic parasite of some kind. From 

 the structure of primary and secondary growths it is 

 necessary to assume that if there is a parasite it must 

 not only incite the cell to division, but also actually 

 be intracellular, for the cells of a secondary distant 

 tumour are the descendants of those that compose the 

 primary tumour. For example, a cancer may arise 

 from the liver. It is composed of liver cells ; it may 

 actually, although in an imperfect way, secrete bile. 

 Such a tumour may be carried to the brain, and there 

 we again find that the tumour is composed, not of 

 brain but of liver cells, and it may actually produce 

 bile. If such a tumour is due to a parasite the latter 

 must be inside the tumour cells. Many attempts have 

 been made to find parasites. It must be admitted, 

 however, that up to the present no one has found a 

 parasite in the cells of a tumour which produces a 

 similar tumour in the homologous or heterologous 

 species. 



(3) The failure to find a parasite led to another 

 theory — that tumours arise from some embryonic 

 aberration. This view is associated with the names 



NO. 2803, VOL. 112] 



of Durante and Cohnheim, and in certain cases is un- 

 doubtedly to be accepted as the probable cause, if it 

 is agreed that there is a high degree of specificity among 

 cells. There is much reason to believe that cells 

 retain their specific characters, or, as Bard has expressed I 

 it, " Omnis cellula e ccllula ejusdem generis." If this 

 is correct, as it appears to be, one can explain the 

 occurrence of heterotopic tumours best upon an 

 embryological basis. Thus the occurrence of a tress 

 of hair, a tooth, a piece of cartilage, and fragments of 

 lung or intestine in a dermoid tumour of the ovar)' of 

 a virgin is explicable best on some embr\'ological 

 aberration. It is impossible to believe that the 

 occurrence of looo teeth in a tumour of the jaw can 

 be produced by a parasite. 



While, however, Cohnheim's theory may explain 

 some growths, there are others which do not come into 

 this category. The degeneration of the process of 

 growth, which is one of the main features of tumours, 

 is evidently some very fundamental process, for 

 growths benign and malignant are found in all animals 

 from fish upwards. Although this fact does not explain 

 the cause of cancer, it dispels many of the foolish 

 theories which have been brought for^s'ard to explain 

 cancer in man. 



Up to the present time, the histological structure 

 of tumours has been very extensively studied all 

 over the world, but it is increasingly apparent that 

 this method alone has great limitations. In con- 

 sequence, it has given way to the study of malignant 

 tumours which can be successfully transplanted from 

 one animal to another of the same species. Many 

 facts connected with the origin and spread of, and 

 immunity to growths have been established by this 

 kind of investigation. 



In more recent times the physiological processes 

 in cancer tissue have been investigated, as well 

 as the production of malignant tumours in animals, 

 by the application of chemical substances like tar or 

 the chemical substances produced by the concurrent 

 development in the animal of certain animal parasites, 

 as was shown by the extended researches of Johannes 

 Fibiger in Copenhagen. 



Another line of work has concerned itself with the 

 growth of tissues in vitro. It is probable that much 

 light will be thrown upon the whole of the blastomatous 

 processes by work of this kind. The field of cancer 

 research in man is limited on account of the fact that 

 he is outside the pale of experimental analysis. Methods 

 of treatment may be tried to cure such a desperate 

 disease, but it is reasonable to demand that there should 

 first be some experimental basis for the treatment. 



The main point, however, is that all over the world 

 the highest class of scientific workers are busily engaged 

 in trying to solve one of Nature's great mysteries which 

 affects both man and almost all known animals. 

 Cancer is a dreadful, inscrutable disease, and, however 

 blunted medical men become from constant associa- 

 tion with other diseases, they never become immune 

 to the sufferings of the cancer patient. Although the 

 main cause of the trouble is unsolved, it is not to 

 be imagined that the research world is standing still. 

 On the contrary', there is everywhere a pulsation which 

 indicates that we are getting nearer the solution of the 

 mystery. ^^ . B. 



