ago 



SCIENCE. 



[Vol. X. No. 254 



series of changes has been evolved by environment, by conditions 

 in persons or in surroundings, until the result of some of these 

 changes becomes self-assertive, and prevails over its heredity so as 

 to secure for a longer or shorter period a fixity of its own. This 

 fixity may be a new disease. 



II. The history of hybrids, the so-called accidents of their occur- 

 rence, and the fertility of hybrids, are such that we are forced to 

 look upon them as new forms of life — as becoming established into 

 an autonomy or individuality of their own. 



The horticulturist in some of the wonderful productions of new 

 plants in the last score of years has come to be familiar with hy- 

 bridisms that wholly obscure origin, and that come to have a fixity 

 of their own as much as some new diseases with which we have to 

 deal, or as much as cases of disease which we cannot trace to a 

 contagious source. 



All this has been greatly emphasized by what we have come to 

 know as the fertility of hybrids. Not over thirty years ago the gen- 

 eral view of botanists was that hybrids were sterile. But so numer- 

 ous are the exceptions, and so abundant have been the results of 

 new cultivations, that this view is fully disproven. Says a recent 

 botanical authority, " Among plants there are many instances of 

 hybrids between species being perfectly fertile, and continuing so 

 for an indefinite period. Experiments during the last twenty-five 

 years have increased the number of such fertile crosses manifold. 

 . . . Fertility of hybrid plants is the rule, and sterility the ex- 

 ception. So far as plants are concerned, there is not the slightest 

 ground for considering sterility as a distinctive bar, separating 

 species. These hybrids come to have a specificity of their own so 

 different from the parentage asto be unrecognizable, and so special- 

 ized as to be permanent." As another expresses it, " The hybrid 

 becomes an individual not responsible to its species." 



Nor is this confined to plants with spores. Some of our most 

 skilful horticulturists are now producing varieties of ferns by hybrid- 

 ism, and every now and then some so-called chance growth or 

 sport shows wide departures. 



The bearing of all this on the parasitic forms of disease is not 

 far to seek. If, as now seems so nearly proven, so much of disease 

 has to do with elementary and minute forms of vegetative life, it is 

 easy to see how the facts of evolution and hybridism have a bearing 

 upon the appearance and propagation of disease. The light of the 

 botanical world and its marvellous revelations as to the actualities 

 and possibilities of the origination of new forms distinct from the 

 parentage, penetrates the hidden sphere of disease-origin, and 

 shows how some diseases cease, how others arise, how some lapse 

 back to their heredity, while others are made permanent or special- 

 ized by their environment, and how others still are hybridized into 

 specific forms, and acquire a fertility and fixity of their own. This 

 range of deviation is so wide as to account for very many of the 

 anomalies of disease, and for the organization, cessation, or modi- 

 fication of form. 



In reply to my inquiry on this particular point, Mr. Mehan, the 

 distinguished botanist of Germantown, Penn., writes me, " All 

 hybrids, that we know by actual experiment are hybrids, are fertile 

 as far as I know, and reproduce their originals just the same as if 

 they were ' original ' species. I think almost every botanist of note 

 believes in abundant, fertile hybrids in nature. Coming down 

 nearer to your own line of thought, I believe it is conceded that all 

 lichens are hybrids between fungi and algffi. It is tenable that new 

 forms of disease are continually coming into existence, which can 

 only arise from new forms of disease-producing plants (micro- 

 scopic fungi) being evolved from older species ; but I do not know 

 whether there is an opinion that these new forms are the result of 

 hybridization or of that natural law of change which seems to be a 

 constituent part of existence — in vegetation, at least." 



In a paper read by Dr. M. W. Taylor before the Epidemio- 

 logical Society of London, April 13, 1887, he notes the fact that 

 many of the fungoid varieties were but " conversions of elementary 

 states of pencillium and oidium. It is also maintained by Zopf (the 

 botanist) that there may be a pleomorphism amid pathogenic 

 micro-organisms, and that there are stages of intermediate forms 

 resulting from the nature of the nutrient media" (see Lancet, 

 May 7, 1S87, pp. 933, 934). 



The view is, vve believe, gaining ground, that harmless micro- 



phytes may become pathogenic, and that the different forms of 

 micro-organisms present have relation to each other, and that the 

 culture-medium in disease, viz., the person and his surroundings, 

 determines the character of the micro-organisms full as much as 

 the micro-organisms determine the character of the disease. 



If the views as to the microphytic origin of most of the com- 

 municable diseases are correct, the study of the laws of this evolu- 

 tion and hybridism is vital. We believe it is in this direction that 

 we are to account for the origin of new diseases, or for such vari- 

 ations in type as obscure or destroy identity. If we can, through 

 this study, arrive at the evidence that in this sense many diseases 

 begin, we have a new department of study, in that we are called 

 upon to define with accuracy how and why this origin takes place, 

 in order that we may thwart or circumvent the conditions. 



If it is the result of evolution through a long series of changes, it 

 behooves us to study the normal, and to watch and record all the 

 gradations by which the unfriendly result is attained, so that, at 

 some stage, we may intercept the progressive and threatening 

 changes that are occurring, or ascertain what condition of the per- 

 son, or what condition of surroundings, constitutes the influence 

 which brings about the change, or provides the fertilizing medium 

 for the disease, and causes it to break forth. If it is the result of a 

 hybridism which occurs spontaneously or rapidly, we need to study 

 precisely what forms of vegetative life thus incline to coalesce, un- 

 der what condition the union occurs, and how their conjunction, 

 development, and fertility are to be interrupted. 



If special conditions of some parts, — as the throat, for instance, 

 — or certain conditions of the secretions, furnish a special soil or 

 culture-fluid for the propagation of low forms of vegetative life, 

 this is to be studied with exactness. 



In each of these lines the same method of technical study and 

 close record and analysis of facts by competent observers which 

 has prevailed in the study of minute plant-life by botanists, and 

 which has obtained in many other sciences, will, in this compara- 

 tively new field of biological and botanical research, accomplish 

 equally valuable results. In it we are attempting to find out how 

 much and under what circumstances micro-organisms imperil 

 human life. 



The practical value of such an inquiry is apparent, for sooner 

 than is the case with most of the studies of nature, the results will 

 be applicable in the prevention and treatment of disease. It will 

 be a great gain if we can come to know, that either under the laws 

 of evolution, or as the result of admixture or hybridism, symptoms 

 and pathological effects become specialized so as to constitute a 

 new disease which maintains its type. 



As examples of how proximity of different diseases may modify 

 symptoms, we have many suggestive facts in the history of disease. 

 Yellow-fever is believed by many to be a mongrel, born on the high 

 seas by admixture of the jungle-fever of Africa with the typhus of 

 the pent-up hold of the filthy vessel. It is not certain that typhoid- 

 fever was not once nearer to typhus, until it came to be called ab- 

 dominal typhus, and then to have modifications because surround- 

 ings and the acquired power of self-propagation gave it an autonomy 

 of its own. 



It is not even now certain that there are not grades of cesspool and 

 other adynamic fevers that will some day declare another well- 

 marked departure from what we now call typhoid, and come to 

 have an individuality of their own. It is not certain, that, when 

 Sydenham treated scarlet-fever and measles as one disease, their 

 lines of difference were as well marked as now. 



Diphtheria so often seems to have a localized origin, and com- 

 mon forms of sore throat are so often seen to pass away from their 

 general into a special type, that it will not be strange if we can 

 come to the law of departure (see views expressed in the Sanitary 

 Record of Aug. 15, 1887, p. 88, and the contribution of Dr. Wor- 

 din, in the Connectictit State Health Report for 1887, that diph- 

 theria results from the special virulence of a micrococcus which is 

 not specific, put present in forms of foul or septic sore throat). 



While typho-malarial fever has no pathognomonic lesion to dis- 

 tinguish it from the ordinary typhoid, yet we do know it has symp- 

 toms to distinguish it. The advances of biological investigation 

 have put us in regions of new possibilities, that do not involve 

 spontaneous generation, but yet do render probable what is equiva- 



