THE MULTIPLICATION OF EFFECTS. 453 



while the forces which determine it are so involved, and at 

 the same time so unobtrusive ; that it is difficult to detect the 

 multiplication of effects which is elsewhere so obvious. 

 Nevertheless, by indirect evidence we may establish our 

 proposition; spite of the lack of direct evidence. 



Observe, first, how numerous are the changes which any 

 marked stimulus works on an adult organism a human be- 

 ing, for instance. An alarming sound or sight, besides 

 impressions on the organs of sense and the nerves, may pro- 

 duce a start, a scream, a distortion of the face, a trembling 

 consequent on general muscular relaxation, a burst of per- 

 spiration, an excited action of the heart, a rush of blood to 

 the brain, followed possibly by arrest of the heart's action 

 and by syncope ; and if the system be feeble, an illness with 

 its long train of complicated symptoms may set in. Simi- 

 larly in cases of disease. A minute portion of the small-pox 

 virus introduced into the system, will, in a severe case, cause, 

 during the first stage, rigors, heat of skin, accelerated pulse, 

 furred tongue, loss of appetite, thirst, epigastric uneasiness, 

 vomiting, headache, pains in the back and limbs, muscular 

 weakness, convulsions, delirium, &c. ; in the second stage, 

 cutaneous eruption, itching, tingling, sore throat, swelled 

 fauces, salivation, cough, hoarseness, dyspnoea, &c. ; and in 

 the third stage, cedematous inflammations, pneumonia, 

 pleurisy, diarrhoea, inflammation of the brain, ophthalmia, 

 erysipelas, &c. : each of which enumerated symptoms is 

 itself more or less complex. Medicines, special foods, better 

 air, might in like manner be instanced as producing multi- 

 plied results. Now it needs only to consider that 

 the many changes thus wrought by one force on an adult 

 organism, must be partially paralleled in an embryo-organ- 

 ism, to understand how here also the production of many 

 effects by one cause is a source of increasing heterogeneity. 

 The external heat and other agencies which determine the 

 first complications of the germ, will, by acting on these, super- 

 induce further complications ; on these still higher and more 



