As the sexual cells of the human body are immortal, like the protozoa, the problem arises if these too be endowed with an immortal soul. Our existing knowledge makes it impossible to doubt that ova and spermatozoa have sensibility in a degree as high as that of the protozoa. The ova shed secretions that arouse the sensibility of the spermatozoa, and the latter, directed by this specific “odour” (the occurrence being known technically as chemotaxis), make their way to the ovum and penetrate it. Some substances, arousing the spermatozoa into activity and movement, attract them, others repel them. The phenomena of chemotaxis were shown for the first time in the case of cryptogams by Pfeffer, the distinguished botanist, and since then the male cells of many plants and different kinds of animals have been proved to possess sensibility. When ova and spermatozoa succeed in conjugating, they produce an individual of the next generation, to which they transmit what Haeckel has called the “cellular soul.”[325] This soul, then, is really immortal, inasmuch as the bodies of the reproductive cells are immortal. Although it is true that our bodies contain elements endowed with immortal souls, it by no means follows that our conscious souls are immortal. In an earlier chapter, I have already pointed out that the psychical phenomena of many of the cells of our body and the cellular souls of these are outside our consciousness. We have no consciousness of the perpetual battle waged by the phagocytes against the microbes that endeavour to obtain a foothold in our tissues. None the less the phagocytes are elements endowed with mobility and sensibility and possessing a cellular soul like that of the protozoa. A woman has no consciousness of the numerous spermatozoa, with their cellular souls, that enter her body, nor of those that fertilise her egg-cells; she is even without consciousness of the much more highly developed soul of the fœtus. A child before birth possesses psychical qualities much more numerous and more perfect than those of the reproductive cells. It is capable of responding to certain sensations and of performing movements. A child, in the later months of its prenatal existence, possesses the senses of touch and taste and, within limits, the sense of sight.[326] This soul is outside the consciousness of the mother. The mother cannot even tell by her consciousness if she bears under her girdle one or two embryonic souls. And so the immortality of the cellular soul has no relation to the problem of death.