BIOLOGY IN ITS WIDER ASPECTS 1231 



preting the differentiation of tissues, more active or more passive; 

 as from the actively ciliated cells so common in lower types, and even 

 lining usefully our own wind-pipes, to the more or less actively 

 contractile cells of muscle tissues, so different in efficiency and power 

 in various phyla, to the passive and encysted cells of cartilage, and 

 their even calcified encystment in bone. Even the amoeboid type — 

 in various comparatively slight, but physiologically important dif- 

 ferentiations — persists in the leucocytes of perivisceral, circulatory, 

 and lymphatic fluids, so familiar throughout the animal kingdom, 

 up to ourselves. And even in the elongated growth and ramifications 

 of developing nerve-cells, despite their supreme physiological com- 

 plexity, do we not see likeness to the development of rhizopod-like 

 pseudopodia? Many embryonic animal forms show more or less of 

 this cell-cycle in the early phases of their development. And the like 

 too in pathological processes. The ciliated cells of the outer epi- 

 dermic layer covering a planarian worm, when exposed to cold, may 

 relapse to unmistakably amoeboid form; and may we not suspect 

 that the too frequent indisposition of those of our own air-tube 

 may be so far in like manner affected ? And as leucocytes may leave 

 the circulation to settle down into passive cells of connective tissue, 

 are they not thereby exhibiting something of the ancestral cell- 

 cycle? And since such connective tissues may resume growth and 

 even show active cell-division, and thus attain to passive tumours — 

 which also may become active in their parent organism — may we 

 not interpret at least one factor in such disease as of reversion to 

 something of the ancestral cell-cycle; yet this interfered with by 

 their surrounding conditions, and these pathologically exciting to 

 and by it. That disease is associated with disturbance of that 

 general co-ordination of the organism which is health, and that the 

 re-establishment of co-ordination is the explanation of the %ns 

 medicatrix naturce, are old and familiar ideas in medicine; ^^et the 

 above conception of the cell-cycle may at least have suggestiveness, 

 and towards other interchanges of biological and medical ideas. 



BIOLOGY AND MEDICINE AGAIN 



The fact is that each profession, each line of occupation, and 

 indeed each age and sex also, has its own familiar and customary 

 thought-world, and does not easily get beyond it, nor readily wel- 

 come and incorporate contributions from others. Thus neither the 

 religious, the political, the administrative or legal training has much 

 contact with even the physical sciences ; while the industrial occupa- 

 tions rarely go beyond these. So biology has been as yet mainly 

 left to the education of the medical profession; but its members are 

 generally too young to master its principles as students, and too 



