;28 



NA TURE 



•^ August 2, 1906 



form the genital passages, and may become renal excretory 

 organs also. The vascular system has not, as it was 

 formerly supposed to have, any connection of origin with 

 the ccelom, but is independent of it, in orij^in and develop- 

 ment, as also are the primitive and superficial renal tubes 

 known as nephridia. These general statements seem to me 

 to cover the most important advance in the general morph- 

 ology of animals which we owe to embryological research 

 in the past quarter of a century.' 



Before leaving the subject of animal morphology I must 

 apologise for my inability to give space and time to a 

 consideration of the growing and important science of 

 anthropology, which ranges from the history of human 

 institutions and language to the earliest prehistoric bones 

 and implements. Let me therefore note here the discovery 

 of the cranial dome of Pithecanthropus in a river gravel 

 in Java — undoubtedly the most ape-like of human remains, 

 and of great age ; and, further, the Eoliths of Prestwich, 

 in the human authorship of which I am inclined to believe, 

 though I should be sorry to say the same of all the broken 

 flints to which the name " Eolith " has been applied. 

 The systematic investigation and record of savage races 

 have taken on a new and scientific character. Such work 

 as Baldwin Spencer's and Haddon's in Australasia furnish 

 examples of what is being done in this way. 



Physiology of Plants and Animals. — Since I have only 

 time to pick the most important advances in each subject 

 for brief mention, I must signalise in regard to the physi- 

 ology of plants the better understanding of the function 

 of leaf-green or chlorophyll due to Pringsheim and to the 

 Russian Timiriaseff, the new facts as to the activity of 

 stomata in transpiration discovered by Horace Brown, and 

 the fixation of free nitrogen by living organisms in the 

 soil and by organisms (Bacillus radicola) parasitic in the 

 rootlets of leguminous plants, which thus benefit by a 

 supply of nitrogenous compounds which they can assimilate. 



Great progress in the knowledge of the chemistry of 

 the living cells or protoplasm of both plants and animals 

 has been made by the discovery of the fact that ferments or 

 enzymes are not only secreted externally by cells, but 

 exist in active and preformed inside cells. Biichner's final 

 conquest of the secret of the yeast-cell by heroic mechanical 

 methods — the actual grinding to powder of these already 

 very minute bodies — first established this, and now 

 successive discoveries of intracellular ferments have led to 

 the conclusion that it is probable that the cell respires by 

 means of a respiratory " oxydase," builds up new com- 

 pounds and destroys existing ones, contracts and accom- 

 plishes its own internal life by ferments. Life thus (from 

 the chemical point of view) becomes a chain of ferment 

 actions. Another most significant advance in animal 

 physiology has been the sequel (as it were) of Bernard's 

 discovery of the formation of glycogen in the liver, a sub- 

 stance not to be excreted, but to be taken up by the blood 

 and lymph, and in many ways more important than the 

 more obvious formation of bile which is thrown out of the 

 gland into the alimentary canal. It has been discovered 

 that many glands, such as the kidney and pancreas and 

 the ductless glands, the suprarenals, thyroid, and others, 

 secrete indispensable products into the blood and lymph. 

 Hence myxoedema, exophthalmic goitre, Addison's disease, 

 and other disorders have been traced to a deficiency or 

 excess of internal secretions from glands formerly regarded 

 as interesting but unimportant vestigial structures. From 

 these glands have in consequence been extracted remark- 

 able substances on which their peculiar activity depends. 

 From the suprarenals a substance has been extracted which 

 causes activity of all those structures which the sympa- 

 thetic nerve system can excite to action : the thyroid yields 

 a substance which influences the growth of the skin, hair, 

 bones, &c. ; the pituitary gland, an extract which is a 

 specific urinary stimulant. Quite lately the mammalian 

 ovary has been shown by Starling to yield a secretion which 

 influences the state of nutrition of the uterus and mammae. 

 Had I time, I might say a great deal more on topics such 

 as these — topics of almost infinite importance; but the fact 

 is that the mere enumeration of the most important lines 

 of progress in any one science would occupy us for hours. 



1 "^ee the introduction to par: ii. of a " Treatise on Zoology," edited by 

 E. Ray Lankester. (London : A. and C. RIacIt.) 



NO I918, VOL. 74] 



Nerve-physiology has inade immensely important advances. 

 There is now good evidence that all excitation of one group 

 of nerve-centres is accompanied by the concurrent inhibition 

 of a whole series of groups of other centres, the activity of 

 which might interfere with that of the group e.xcited to action. 

 In a simple reflex flexure of the knee the motor-neurones 

 to the fle.Kor muscles are excited, but concurrently the motor- 

 neurones to the extensor muscles are thrown into a state 

 of inhibition, and so equally with all the varied excita- 

 tions of the nervous system controlling the movements and 

 activities of the entire body. 



The discovery of the continuity of the protoplasm through 

 the walls of the vegetable cell by means of connecting 

 canals and threads is one of the most startling facts dis- 

 covered in connection with plant-structure, since it was held 

 twenty years ago that a fundamental distinction between 

 animal and vegetable structure consisted in the boxing-up 

 . or encasement of each vegetable cell-unit in a case of 

 cellulose, whereas animal cells were not so imprisoned, but 

 freely communicated with one another. It perhaps is on 

 this account the less surprising that lately something like 

 sense-organs have been discovered on the roots, stems, and 

 leaves of plants, which, like the otocysts of some animals, 

 appear to be really " statocytes," and to exert a varying 

 pressure according to the relations of these parts of the 

 plant to gravity. There is apparently something resem- 

 bling a perception of the incidence of gravity in plants which 

 reacts on irritable tissues, and is the explanation of the 

 phenomena of geotropism. These results have grown out 

 of the observations of Charles Darwin, followed by those 

 of F. Darwin, Haberlandt, and Nemec. 



A few words must be said here as to the progress of our 

 knowledge of cell-substance, and what used to be called the 

 protoplasm question. We do not now regard protoplasm 

 as a chemical expression, but, in accordance with von 

 Mohl's original use of the word, as a structure which holds 

 in its meshes many and very varied chemical bodies of great 

 complexity. Within these twenty-five years the " centro- 

 some " of the cell-protoplasm has been discovered, and a 

 great deal has been learnt as to the structure of the 

 nucleus and its remarkable stain-taking bands, the chromo- 

 somes. We now know that these bands are of definite 

 fixed number, varying in different species of plants and 

 animals, and that they are halved in number in the repro- 

 ductive elements — the supermatozoid and the ovum — so 

 that on union of these two to form the fertilised ovum (the 

 parent cell of all the tissues), the proper specific number 

 is attained. It has been pretty clearly made out by cutting 

 up large living cells — unicellular animals — that the body of 

 the cell alone, without the nucleus, can do very little but 

 move and inaintain for a time its chemical status. But 

 it is the nucleus which directs and determines all definite 

 growth, movement, secretion, and reproduction. The 

 simple protoplasm, deprived of its nucleus, cannot form a 

 new nucleus — in fact, can do very little but exhibit irrita- 

 bility. I am inclined to agree with those who hold that 

 there is not suflicient evidence that any organism exists at 

 the present time which has not both protoplasm and nucleus 

 — in fact, that the simplest form of life at present existing 

 is a highly complicated structure — a nucleated cell. That 

 does not imply that simpler forms of living matter have 

 not preceded those which we know. AVe must assume that 

 something more simple and homogeneous than the cell, with 

 its differentiated cell-body or protoplasm, and its cell kernel 

 or nucleus, has at one time existed. But the various sup- 

 posed instances of the survival to the present day of such 

 simple living things — described by Haeckel and others — 

 have one bv one yielded to improved methods of micro- 

 scopic examination and proved to be differentiated into 

 nuclear and extra-nuclear substance. 



The question of " spontaneous generation " cannot be said 

 to have been seriously revived within these twenty-five 

 years. Our greater knowledge of minute forms of life, and 

 the conditions under which they can survive, as well as 

 our improved microscopes and rnethods of ciperiment and 

 observation, have made an end of the arguments and 

 instances of simposed abiogenesis. The accounts which 

 have been published of " radiobes," minute bodies arising in 

 fluids of organic origin when radium salts have been allowed 

 to mix in minute quantities with such fluids, are wanting 

 in precision and detail, but the microscopic particles which 



