i8 



NATURE 



[September 5, 191 2 



circulate in the blood and effect changes in cells of 

 distant parts of the body. It is through these hor- 

 mones that the secondary sexual characters, such as 

 the comb and tail of the cock, the mane of the lion, 

 the horns of the stag, the beard and enlarged larynx 

 of a man, are produced, as well as the many differ- 

 ences in form and structure of the body which are 

 characteristic of the sexes. The dependence of these 

 so-called secondary sexual characters upon the state 

 of development of the reproductive organs has bei ji 

 recognised from time immemorial, but has usually 

 been ascribed to influences produced through the 

 nervous system, and it is only in recent years that 

 the changes have been shown to be brought about 

 by the agency of internal secretions and hormones, 

 passed from the reproductive glands into the cir- 

 culating tlood.-' 



Chemical Nature oj Hormones. 



It has been possible in only one or two instances 

 to prepare and isolate the hormones of the internal 

 secretions in a sufficient condition of purity to subject 

 them to analysis, but enough is known about them to 

 indicate that they are organic bodies of a not very 

 complex nature, far simpler than proteins and even 

 than enzymes. Those which have been studied are 

 all dialysable, are readily soluble in water but in- 

 soluble in alcohol, and are not destroyed by boiling. 

 One at least — that of the medulla of the suprarenal 

 capsule — has been prepared synthetically, and when 

 their exact chemical nature has been somewhat better 

 elucidated it will probably not be difficult to obtain 

 others in the same way. 



From the above it is clear that not only is a co- 

 ordination through the nervous system necessary 

 in order that life shall be maintained in a 

 normal condition, but a chemical coordination 

 is no less essential. These may be indepen- 

 dent of one another ; but, on the other hand, 

 they may react upon one another. For it can be 

 shown that the production of some at least of the 

 hormones is under the influence of the nervous system 

 (Biedl, ./Vsher, Elliott); whilst, as we have seen, some 

 of the functions of the nervous system are dependent 

 upon hormones. 



Protective Chemical Mechanisms. — Toxins and 

 .Antitoxins. 

 Time will not permit me to refer in any but the 

 briefest manner to the protective mechanisms which 

 the cell-aggregate has evolved for its defence against 

 disease, especially disease produced by parasitic micro- 

 organisms. These, which belong with few excep- 

 tions to the Protista, are without doubt the most 

 formidable enemies which the multicellular Metazoa, 

 to which all the higher animal organisms belong, 

 have to contend against. To such micro-organisms are 

 due, inter alia, all diseases which are liable to become 

 epidemic, such as anthrax and rinderpest in cattle, 

 distemper in dogs and cats, smallpox, scarlet fever, 

 measles, and sleeping sickness in man. The 

 advances of modern medicine have shown that the 

 symptoms of these diseases — the disturbances of 

 nutrition, the temperature, the lassitude or excite- 

 ment, and other nervous disturbances — are the effects 

 of chemical poisons (toxins) produced by the micro- 

 organisms and acting deleteriously upon the tissues 

 of the body. The tissues, on the other hand, en- 

 deavour to counteract these effects by producing other 

 chemical substances destructive to the micro- 

 organisms or antagonistic to their action : these are 

 known as anti-hodies. Sometimes the protection takes 

 the form of a subtle alteration in the living substance 



•-* The evidence !s to be found in F. H. A. Marshall,"." The Physiology 

 of Reproduction,'" 



NO. 2236, VOL. go] 



of the cells which renders them for a long time, or 

 even permanently, insusceptible (immune) to the 

 action of the poison. Sometimes certain cells of the 

 body, such as the white corpuscles of the blood, eat 

 the invading micro-organisms and destroy them 

 bodily by the action of chemical agents within their 

 protoplasm. The result of an illness thus depends 

 upon the result of the struggle between these oppos- 

 ing forces — the micro-organisms on the one hand 

 and the cells of the body on the other — both of which 

 fight with chemical weapons. If the cells of the 

 body do not succeed in destroying the invading 

 organisms, it is certain that the invaders will in 

 the long run destroy them, for in this combat no 

 quarter is given. Fortunately we have been able, by 

 the aid of animal experimentation, to acquire some 

 knowledge of the manner in which we are attacked 

 by micro-organisms and of the methods which the 

 cells of our body adopt to repel the attack, and the 

 knowledge is now extensively utilised to assist our 

 defence. 



Parasitic Nature of Diseases. 

 For this purpose protective serums or anti- 

 toxins, which have been formed in the blood of other 

 animals, are employed to supplement the action of 

 those which our own cells produce. It is not too 

 much to assert that the knowledge of the parasitic 

 origin of so many diseases and of the chemical agents 

 which on the one hand cause, and on the other 

 combat, their symptoms, has transformed medicine 

 from a mere art practised empirically into a real 

 science based upon experiment. The transformation 

 has opened out an illimitable vista of possibilities 

 in the direction not only of cure, but, more important 

 still, of prevention. It has taken place within the 

 memory of most of us who are here present. And 

 only last February the world was mourning the death 

 of one of the greatest of its benefactors — a former 

 President of this .Association -" — who, by applying this 

 knowledge to the practice of surgery, was instru- 

 mental, even in his own lifetime, in saving more 

 lives than were destroyed in all the bloody wars of 

 the nineteenth century ! 



Senescence and Death. 

 The question has been debated whether, if all acci- 

 dental modes of destruction of the life of the cell 

 could be eliminated, there would remain a possibility 

 of individual cell life, and even of aggregate cell life, 

 continuing indefinitely ; in other words. Are the 

 phenomena of senescence and death a natural and 

 necessary sequence to the existence of life? To most 

 of my audience it will appear that the subject is not 

 open to debate. But some physiologists {e.g. 

 Metchnikoff) hold that the condition of senescence is 

 itself abnormal ; that old age is a form of disease or 

 is due to disease, and, theoretically at least, is capable 

 of being eliminated. We have already seen that 

 individual cell life, such as that of the white blood- 

 corpuscles and of the cells of many tissues, can imder 

 suitable conditions be prolonged for days or weeks 

 or months after general death. Unicellular organisms 

 kept under suitable conditions of nutrition have been 

 observed to carry on their functions normally for 

 prolonged periods and to show no degeneration such 

 as would accompany senescence. They give rise by 

 division to others of the same kind, which also, under 

 favourable conditions, continue to live, to all appear- 

 ance indefinitely. But these instances, although they 

 indicate that in the simplest forms of organisation 

 existence may be greatly extended without signs of 

 decav, do not furnish conclusive evidence of indefinite 



'^ Lord Lister was President at Liverpool in i8g6. 



