The histochemical characterization of articular cartilage from the joint surfaces of the hind limbs of puppies up to twenty-five weeks of age and twelve weeks following the denervation of one extremity was examined. The animals were divided into four groups, primarily according to age and secondarily according to the length of time following the denervation. The chemical changes occurring in the atrophied tissues appeared rapidly at first, progressed, and then seemed to remain somewhat stationary. In all of

the groups, the extracellular-solid mass decreased as a result of some decrease in the connective-tissue solids and a marked decrease in the chondroitin sulphate. The extracellular water increased markedly as a result of large increases in the ultrafiltrate water. The water of the chondrocytes (the intracellular water) decreased in volume as well as in percentage.

Some of the salient points gathered from observations on articular cartilage which had atrophied following denervation of the extremity were:

1 . An increase in total water content of the cartilage, resulting from increases in the ultrafiltrate water in the extracellular compartment of the tissue;

2. A marked decrease in the chondroitin sulphate mass (not only was the decrease found when 100 grams of the cartilage solids was considered hut also when a kilogram of fresh cartilage was considered);

3. A decrease in the connective-tissue mass expressed per kilogram of fresh tissue, which was the result of dilution of the extracellular compartment with large volumes of ultrafiltrate water;

4. Percentage of water in the chondrocytes decreased in value from an average normal of 80 to 74 in the young puppies with four weeks of atrophy following denervation and from 74 in the controls to as low as 60 in the older puppies with up to twelve weeks of atrophy.