The paper by Maurice A. Biot presents a generalized theory of acoustic propagation in porous dissipative media, extending previous work to include anisotropy, viscoelasticity, and solid dissipation. The author introduces the concept of a "viscoelastic operator" to refine the analysis of fluid motion in pores, which is evaluated using Lagrangian and variational methods. Various dissipative models are discussed, and the corresponding operators and relaxation spectra are derived. The theory incorporates physical-chemical phenomena, including surface effects and interfacial forces, and addresses thermoelastic dissipation and electrokinetic effects. The paper also discusses scaled-model tests and the use of Lagrangian equations to derive the viscoelastic operator in both low- and high-frequency ranges. The theory is applicable to both isotropic and anisotropic media, and the author provides illustrative viscoelastic models to demonstrate the application of the theory to complex physical-chemical phenomena.The paper by Maurice A. Biot presents a generalized theory of acoustic propagation in porous dissipative media, extending previous work to include anisotropy, viscoelasticity, and solid dissipation. The author introduces the concept of a "viscoelastic operator" to refine the analysis of fluid motion in pores, which is evaluated using Lagrangian and variational methods. Various dissipative models are discussed, and the corresponding operators and relaxation spectra are derived. The theory incorporates physical-chemical phenomena, including surface effects and interfacial forces, and addresses thermoelastic dissipation and electrokinetic effects. The paper also discusses scaled-model tests and the use of Lagrangian equations to derive the viscoelastic operator in both low- and high-frequency ranges. The theory is applicable to both isotropic and anisotropic media, and the author provides illustrative viscoelastic models to demonstrate the application of the theory to complex physical-chemical phenomena.