26

67

Chapter I

Having referred to the act of sucking, I may add that this complex movement, as well as the alternate protrusion of the forefeet, are reflex actions; for they are performed if a finger moistened with milk is placed in the mouth of a puppy, the front part of whose brain has been removed.*(14) (17) It has recently been stated in France, that the action of sucking is excited solely through the sense of smell, so that if the olfactory nerves of a puppy are destroyed, it never sucks. In like manner the wonderful power which a chicken possesses only a

[Expression, p. 47.]

few hours after being hatched, of picking up small particles of food, seems to be started into action through the organ sense of hearing; for with chickens hatched by artificial heat, a good observer found that "making a noise with the finger-nail against a board, in imitation of the hen-mother, first taught them to peck at their meat."(15) (18)

Passion

I will give here only one other instance of an habitual and purposeless movement. The Sheldrake (Tadorna) feeds on the sands left uncovered by the tide, and when a worm-cast is discovered, "it begins patting the ground with its

[Expression, p. 47.]

21

62

Chapter I

although the road is quite open and the distance great. Again dogs of all kinds when intently watching and slowly approaching their prey, frequently keep one of their fore-legs doubled up for a long time, ready for the next cautious step; and this is eminently characteristic of the pointer. But

[slip of paper pasted on:] from habit they behave in exactly the same manner whatever they are closely attending. (Fig. 4). I have seen a dog at the foot of a high wall, listening attentively to a sound on the opposite side, with one leg doubled up; & in this case these could have been no

[21v]

intention of making a cautious approach. or a spring.

Dogs after voiding their excrement often make with all four feet a few scratches backwards, even on a bare stone pavement, as if for the purpose of covering up with earth their excrement, in nearly the same manner as do cats. Wolves and jackals behave in the Zoological Gardens in exactly the same manner, yet, as I am assured by the keepers, neither wolves, jackals, nor foxes nor dogs, when they have the means of doing so, ever cover up their excrement, any more than do dogs. All these animals, however, bury superfluous food. Hence, if we rightly understand the meaning of the above

[Expression, p. 44.]

17A

58

Chap. I

(lead on) In such cases, some explanation, quite distinct from habit, will have to be discovered. The radiation of nerve-force from certain certain strongly-excited nerve-cells to other connected cells, as in the case of a bright light on the retina causing a sneeze, may perhaps aid us in understanding how some certain reflex actions were first developed originated. A radiation of nerve-force of this kind, if it induced any caused a movement tending to lessen a the primary irritation, as in the case of the contraction of the iris which prevents from too bright a much light from falling on it the retina, might afterwards have been taken advantage of and modified

[Expression, p. 41.]

[17Av]

we shall have presently to return in a future chapter

The contraction of the iris, when the retina is acted on stimulated by a bright light, is another instance of a movement, which it appears cannot possibly have been at first voluntarily gained performed afterwards fixed by habit; for the iris is not known to be under the conscious control of the will in any animal. It is of course possible, however improbable, that the iris may primordially have been acted on by voluntary muscles, which subsequently became changed in character, so as to be independent of the will. Some

[Expression, p. 41.]

[10?]

57

Chapter I

, as we have seen is accompanied by the blinking of the eyelids so as to protect the eyes, which are the most tender and sensitive organs of the body; and it is, I believe always accompanied by a sudden and forcible inspiration, which as we shall hereafter see, is the natural preparation for any violent effort. But when a man or horse starts his heart beats wildly against his ribs, and here it may be truly said we have an organ which has never been under the constant control of the will, partaking in the general reflex movements of the body. To this point, however,

[Expression, p. 41.]

[Proof sheet of Insectivorous plants, p. 242.]

[Proof sheet of Insectivorous plants, p. 449.]