At the head of these important phenomena of progressive transmission, we may mention the _law of adapted or acquired transmission_. In reality it asserts nothing more than what I have said above, that in certain circumstances the organism is capable of transmitting to its descendants all the qualities which it has acquired during its own life by adaptation. This phenomenon, of course, shows itself most distinctly when the newly acquired peculiarity produces any considerable change in the inherited form. This is the case in the examples I mentioned in the preceding chapter as to transmission in general, in the case of the men with six fingers and toes, the porcupine men, copper beeches, weeping willows, etc. The transmission of acquired diseases, such as consumption, madness, and albinism, likewise form very striking examples. Albinoes are those individuals who are distinguished by the absence of colouring matter, or pigments, in the skin. They are of frequent occurrence among men, animals, and plants. In the case of animals of a definite dark colour, individuals are not unfrequently born which are entirely without colour, and in animals possessing eyes, this absence of pigment extends even to the eyes, so that the iris of the eye, which is commonly of a bright or intense colour, is colourless, but appears red, on account of the blood-vessels being seen through it. Among many animals, such as rabbits and mice, albinoes with white fur and red eyes are so much liked that they are propagated in great numbers as a special race. This would be impossible were it not for the law of the transmission of adaptations. Which of the changes acquired by an organism are transmitted to its descendants, and which are not, cannot be determined _à priori_, and we are unfortunately not acquainted with the definite conditions under which the transmission takes place. We only know in a general way that certain acquired qualities are much more easily transmitted than others, for example, more easily than the mutilations caused by accidents. These latter are generally not transmitted by inheritance, otherwise the descendants of men who have lost their arms or legs would be born without the corresponding arm or leg; but here, also, exceptions occur, and a race of dogs without tails has been produced by consistently cutting off the tails of both sexes of the dog during several generations. A few years ago a case occurred on an estate near Jena, in which by a careless slamming of a stable door the tail of a bull was wrenched off, and the calves begotten by this bull were all born without a tail. This is certainly an exception; but it is very important to note the fact, that under certain unknown conditions such violent changes are transmitted in the same manner as many diseases.